Corneal tissue is damaged by various factors, such as internal factors including decreased amounts of tears, reduction in corneal sensitivity, diabetes, and microbial infection; and external factors including drugs, injury, contact lenses, and light. Corneal disorders caused by such damages can lead to blindness in severe cases, and even in mild cases, corneal disorders can become severe when the damaged site is infected with a microorganism. It is thus extremely important to perform appropriate treatment for corneal disorders, or prevent corneal disorders by removing internal factors.
Dry eye is a disease that leads to corneal disorders due to decreases in the amount of tears or changes in the quality of tears. In recent years, the number of dry eye patients has been growing with increases in, for example, VDT operations and contact lens wearers, and is said to have reached about 8 million including potential patients.
Reduction in corneal sensitivity is said to continue generally for about 3 weeks to 1 year after corneal surgeries such as photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), laser assisted subepithelial keratectomy (LASIK), and corneal transplantation, because corneal nerves are severed by such surgeries. It is known that reduction in corneal sensitivity induces lacrimal hyposecretion, which leads to a corneal disorder, and ultimately causes a lacrimal gland disorder, and that these occur in a vicious cycle (NPL 1).
Angiopoietin-like proteins (ANGPTLs) are known as proteins structurally similar to angiopoietin. In humans, seven kinds of angiopoietin-like proteins have been identified to date. It has been reported that ANGPTL7, which is one of them, is expressed in the corneal stroma, the Bowman's membrane, the sclera, the Schlemm's canal endothelium, the trabecular meshwork, and the lamina cribrosa of the optic nerve in ocular tissue. It has been reported that ANGPTL7 have, for example, the following functions: ANGPTL7 is involved in maintaining the transparency of the cornea (NPL 2); ANGPTL7 is involved in tumor growth suppression and angiogenesis suppression (NPL 3); and that ANGPTL7 suppresses invasion of blood vessels into the cornea (NPL 4).
However, the effect of ANGPTL7 on corneal disorders such as corneal epithelial disorder, dry eye, and reduction in corneal sensitivity has not been known at all.